A chair of this kind can be known, for example, from EP2173218B1.
In general, office chairs of newest kinds have a so-called synchronous mechanism in which correlative movement of a seat and a backrest at the time of inclination of the backrest is generated such that a seat rear region also can be inclined simultaneously to the inclination of the backrest.
The synchronous mechanism is usually integrated in a support unit (referred to as a base support unit, here) on the seat lower side. The support unit is usually fastened on the support arm and connected to a pillar therethrough. Basically, synchronous mechanisms of various configurations are known. Further, a mechanism having an automatic weight adjustment function is also known in which a restoring force acting on the backrest is automatically adjusted in accordance with the actual body weight of a user of the present time. An example of an office chair having such a synchronous mechanism and an automatic weight adjustment function is known in EP2173218B1 described above.